Motor vehicles are equipped with airbags to ensure safety of occupants.
An airbag is designed so that, in a collision accident of a motor vehicle, a sensor, receiving an impact of the collision, becomes activated to cause a high-temperature and high-pressure gas to be generated within the airbag, and the airbag is instantly inflated by the gas to protect an occupant's face or forehead at the time of the collision.
Airbags are typically made by producing a base cloth in which a resin such as silicone is applied to or layered on a woven fabric cloth made of a plain woven fabric that uses a Nylon 6/6 filament yarn or a Nylon 6 filament yarn of 100 to 1000 dtex to improve characteristics such as heat resistance, flame retardance, or air shut-off property, and then cutting and sewing the cloth into a bag body.
Furthermore, there is a so-called “non-coated” cloth obtained for use by weaving synthetic fiber filament yarns of polyamide fiber, polyester fiber or the like in high density without providing resin so that the amount of air permeation through the textile is made small.
It is to be noted herein that the woven fabric for an airbag is required to have high strength and low air permeability since, in a collision accident of a motor vehicle, the airbag is to be instantly inflated to protect an occupant's face or forehead at the time of the collision.
Therefore, the woven fabric for airbags needs to be a woven fabric that employs yarns of higher strength and that is high in density compared to woven fabrics for ordinary clothing.
Typically, when such a high-density woven fabric is woven, the amount of movement of the weaving shed at the cloth fell from the most advanced position of the reed to the warp yarn send-out side becomes larger as the weft density becomes higher, due to woven fabric design, as in a plain woven structure where the warp yarns and the weft yarns are 470 dtex and the warp and weft woven fabric densities are 55 yarns per inch (2.54 cm) for both the warp and weft and the like.
Due to this, inconveniences at the time of weaving as mentioned in (a) to (d) below occur.
(a) At the time of reed beating, the woven fabric near the cloth fell undergoes a bumping phenomenon so that it becomes hard to obtain a woven fabric having a desired weft density.
(b) After the weft yarn is beaten, the weft yarn is cut at each of left and right end portions of the cloth fell by a cutter. At that time, the cut weft yarn loses a hold and becomes free, the weft yarn crimp at each of two selvage end portions of the base cloth becomes large and, therefore, the warp yarn crimp at each selvage end portion becomes smaller so that the warp yarn tension in both selvage portions declines. Therefore, the warp's holding force for the weft declines so that the weaving sheds at both selvage portions of the cloth fell recede. As a result, fluffing due to the warp yarn looseness in the selvage portions is induced so that weaving cannot be stably performed.(c) If the weaving machine rotation speed is made high, a phenomenon in which the weaving sheds of the selvage end portions recede appears more conspicuously. Due to the warp yarn looseness in the base cloth selvage portions, a selvage waving in which a cloth length difference between the selvage portions and a central portion occurs and the selvage end portions become wavy occurs as an essential problem. A base cloth for airbags is cut, sewed, and then made into a bag body. To maximally effectively utilize the base cloth for airbags, a cutting pattern is designed such that, usually, even the selvage end portions or the vicinities thereof are used. Since ends of a cut piece easily unravel, occurrence of selvage waving in the vicinity of a selvage end portion causes poor cutting to occur so that a desired accurate shape as an airbag cannot be obtained and a necessary function will not be obtained.(d) Selvage waving in a gray fabric compromises the processing passing property at the time of rolling and also in the subsequent scouring and setting steps, and also becomes a cause of occurrence of wrinkles. When resin coating is provided, the selvage waving compromises the processing passing property in the coating step, and also causes problems of occurrence of unevenness in the amount of application of the coating resin and wrinkles.
In relation to the foregoing inconveniences (a) to (d), as one of various attempts to prevent the selvage slack resulting from weaving, in particular, a method in which, in a base cloth for airbags made of a synthetic fiber woven fabric, the fineness of the warp yarns of the selvage portions of the woven fabric is finer than the fineness of the warp yarns of a main body portion of the base cloth has been proposed (Japanese Unexamined Patent Publication (Kokai) No. 10-236253). Furthermore, methods in which additional yarns are inserted besides binding yarns or the structure of the binding yarns is changed have been proposed (Japanese Unexamined Patent Publication (Kokai) No. 2001-355143, Japanese Unexamined Patent Publication (Kokai) No. 2002-212856, and Japanese Unexamined Patent Publication (Kokai) No. 2002-69790).
At this time when cost competitiveness is required, weaving machines are operated at increased speed and the width of an object woven fabric is increased. In response to this, however, when a high-density woven fabric is woven, the means as proposed above are not able to sufficiently tighten the weft yarns if the tension of the weft yarns at the time of being run is increased in connection with the increased speed of operation of the weaving machine. This results in a decline in the warp yarn tension in the selvage portions. Then, there is a problem that fluff occurs due to break of a single yarn of the warp, leading to an increased number of times of stop of the weaving machine and a decline in the weaving performance. Furthermore, there is also a problem of the selvage waving becoming great.
In view of the shortcomings of the related-art woven fabrics and production processes therefor, it could be helpful to provide a woven fabric and a process of producing the woven fabric in which when a high-density woven fabric is woven at high speed, recession of the weaving sheds in the selvage end portions is restrained and, when necessary, the selvage waving is lessened.